R and PostgreSQL - Writing data?

Dear all,

Sorry if this isn't quite the right place, but it's the first time
I've posted here. My issue is to do with writing to a PostgreSQL
database from within R. My situation is best explained by some R code
to start:

#Connect to the database
con <- dbConnect(PostgreSQL(), user="postgres", password="password",
dbname="database")

#Get some data out of the database.
ucam_no2$original_data <- dbGetQuery(con, "select ucam_no2 FROM table")

This returns say 10000 rows of data, but there is only data in about
half of those rows. What I want to do is interpolate the missing data
so I do this:

#Generate some data
ucam_no2$interpolated_data <- na.approx(ucam_data$ucam_no2, na.rm = FALSE)

This works well and I now have 10000 rows of data with no empty cells.
I now want to write this back into my PostgresSQL database. Into the
same row that I took the data from in the first place. But I don't
know how. I can write to a new table with something like the below,
but what I'd really like to do is put the data back into the table I
got it from.

# Try to write the data back
dbWriteTable(con, "new_data", ucam_no2$interpolated_data)

Thanks

James